For anyone who lost a wallet file, or might be faced in the future to hard drive failures or accidents and mistakes, it is worth to note that photorec just added support for .wallet files in its 6.14 release published last month.

For those who don't know testdisk and photorec, they are certainly one of the most, if not the most advanced software for data recovery. It was already possible to tweak photorec to make such recovery possible, but now it is part of the software.

So if you hear someone having troubles, this might be a very good resource.